Phacoemulsification system with handpiece simulator

ABSTRACT

A phacoemulsification system is provided, including an ultrasonic phacoemulsification handpiece and a handpiece driver. A handpiece simulator is provided to analyze the performance characteristics of the handpiece driver. The simulator is selectively coupled in a feedback loop with the driver so as to receive drive signals from the driver and return a feedback signal to the driver in the same manner as a handpiece. The simulator detects the frequency and voltage characteristics of the signal provided by the handpiece driver and on the basis thereof generates a feedback signal for return to the handpiece driver. The simulator can exercise the response of the driver dynamically by controllably varying the frequency of the feedback signal. The simulator may be constructed in either analog or microprocessor-based form. In the latter case, the microprocessor can determine whether the drive signals are within acceptable limits, and displays to the user the nature of unacceptable performance.

This invention relates to systems for performing surgery through theultrasonic emulsification of tissue and, in particular, to circuit whichelectronically simulates a handpiece which ultrasonically emulsifiestissue.

Phacoemulsification handpieces are commonly used in surgery for theremoval of tissue and other bodily materials. In opthalmic surgery suchhandpieces are widely used to remove cataracts from the eye. Thehandpiece is energized by a piezoelectric stack which vibrates theworkpiece connected at the end of the handpiece. The piezoelectric stackwill ultrasonically vibrate the workpiece in small amplitudeoscillations at a frequency of many thousand kilohertz. When thevibrating tip of the workpiece contacts a cataract, the cataract tissueis chopped into fine pieces, which can be flushed and removed throughirrigation of the surgical site and aspiration of the emulsifiedmaterial. Such removal of cataracts through phacoemulsification isefficient, precise, and enables removal of the cataract withoutsignificant damage to surrounding eye tissue.

A phacoemulsification handpiece is conventionally powered by a handpiecedrive instrument. The handpiece is detachable from the instrument sothat it can be sterilized, and to enable the use of different types ofhandpieces and workpieces with the same drive instrument. Typically thedrive instrument provides a controllable energizing signal to thepiezoelectric stack which vibrates the workpiece. The drive instrumentalso receives a feedback signal from a second piezoelectric stack to therear of the drive stack. The feedback signal is sensed as a measure ofthe operation of the handpiece and the drive signal adjusted in responseto variances of the feedback signal. This completes a feedback loop ofthe two piezoelectric stacks and the circuitry in the drive instrument,enabling the circuitry to continually monitor and adjust the performanceof the handpiece during surgery.

However, in such a feedback loop diagnosis of a failure is difficultwhen an element of the feedback loop fails or suffers from deterioratingperformance. Once an element in the loop fails, the performance of theentire loop is affected. All that the surgeon knows is that his surgicalsystem is inoperative or ineffective. It would be desirable in such asituation to enable the surgeon to be able to diagnose the systemfailure, and at least be able to determine whether the failure is in thehandpiece or the drive circuitry. If the surgeon was able to determinethat the drive circuitry was not the source of the problem, forinstance, the surgeon could detach the defective handpiece and replaceit with a new one, knowing that the drive circuitry was operatingproperly and that surgery could proceed with the use of the newhandpiece.

In accordance with the principles of the present invention, a handpiecesimulator is provided which enables diagnosis of the drive circuitry ofa phacoemulsification handpiece. The simulator is preferablyincorporated in the same instrument as the drive circuitry, where it isavailable to diagnose the handpiece drive circuitry any time a systemfailure occurs or is suspected. When such a failure occurs, the drivesignal output and the feedback signal input of the drive circuitry areconnected to the simulator. The simulator receives the drive signal andin response thereto generates a feedback signal in the same manner as aphacoemulsification handpiece. The simulator in this environment alsodevelops an output signal to inform the user as to the quality ofoperation of the handpiece drive circuitry. The output signal will tellthe user if the drive circuitry is defective and in need of repair, orwhether the drive circuitry is operating properly, in which case thehandpiece is the source of the problem. In a preferred embodiment thehandpiece simulator would automatically perform a check of the drivecircuitry each time the instrument is initially energized, and wouldalso be activatable under user control if a failure occurs during use ofthe instrument. The simulator would also be useful in a stand-aloneenvironment by service personnel when diagnosing failures inphacoemulsification handpiece systems.

In the drawings:

FIG. 1 is a block diagram of a phacoemulsification handpiece systemconstructed in accordance with the principles of the present invention;

FIG. 2 is a block diagram of the phacoemulsification handpiece simulatorof the system of FIG. 1;

FIG. 3 is a detailed description in schematic and block diagram form ofthe handpiece simulator of FIG. 2; and

FIG. 4 illustrates an embodiment of the present invention utilizing amicroprocessor-based controller.

Referring first to FIG. 1, a phacoemulsification handpiece systemconstructed in accordance with the principles of the present inventionis shown. A handpiece 10 is shown, which generally resembles a thickpencil. A detachable workpiece 12 is mounted at the distal end of thehandpiece. The workpiece 12 is vibrated at ultrasonic frequencies by apiezoelectric drive stack 14 located in the handle portion of thehandpiece. In the illustration of FIG. 1 the workpiece 12 is hollow witha tapered tip 18. In use, the surgical site is infused with a flow ofsolution, and tissue which is emulsified by the vibrating tip isaspirated through the hollow workpiece. The arrows I and A at theproximal end of the handpiece schematically represent the connection ofirrigation and aspiration lines to the handpiece.

The ultrasonic vibrations of the piezoelectric stack 14 are transmittedto the workpiece 12 through intervening connecting elements of thehandpiece. Conventionally the ultrasonic waves have a nodal point whichforms the connection between the inner, vibrating members of thehandpiece and the handpiece case which is held by the user. Byconnecting the case at the nodal point, the vibrations transmitted tothe user's hand are greatly diminished.

Located proximal the stack 14 is a second piezoelectric stack 16, whichalso receives ultrasonic vibrations generated by the drive stack 14. Inresponse to the receipt of these vibrations the second stack 16generates an electrical signal which is fed back to the circuitry of thehandpiece drive module 20. The signal produced by the stack 16 is thus ameasure of the performance of the drive stack and the handpiece, and isused by the circuitry in the module 20 as a feedback signal toconstantly adjust and control the drive signal applied to the drivestack 14.

The module 20 includes handpiece driver circuitry 30 which responds tothe settings of controls, such as the illustrated intensity control,power control, and frequency control, and the feedback signal generatedby the second stack 16 to develop a drive signal for the drive stack 14of the handpiece. In the embodiment of FIG. 1 the handpiece driver 30 isconnected to the drive stack 14 of the handpiece by a cable 19a, and thefeedback signal is returned to the driver 30 by a cable 19b. Thesecables are detachable to enable the connection of various handpieces tothe drive module. The drive and feedback signals are connected to cables19a, 19b through the terminals 1A, 1C and 2A, 2C of two switches 1 and 2when the arms of the switches are set as shown in FIG. 1. The handpiecedriver circuitry is conventional, and may be of the type presentlyavailable in the Site TXR™ Phaco module available from SiteMicrosurgical Systems of Horsham, Pa.

In accordance with the principles of the present invention the module 20also includes a handpiece simulator 40. The handpiece simulator 40 iscapable of receiving the handpiece drive signal from the driver 30 and,in response thereto, producing a commeasurate feedback signal. Thehandpiece simulator 40 may be switched by resetting switches 1 and 2 totheir alternate positions to connect the simulator to the driver. Undercontrol of a system controller 50, which in the preferred embodimentwould include a microprocessor, switches 1 and 2 are reset to connectthe simulator to the driver when the module is initially energized, orunder manual control by the user whenever the user suspects a systemmalfunction. By measuring signal levels at various test points of thesimulator, as discussed below, the controller determines whether theperformance of the handpiece driver is within proper limits, anddisplays the results of this determination on a display 52.

FIG. 2 is a more detailed block diagram of the handpiece simulator 40 ofFIG. 1. At its input the simulator receives the handpiece drive signalfrom the driver 30. This signal is applied to an impedance element 42,at which measurements can be taken of the power delivered by the driver.Following the impedance element 42 the drive signal is processed by twoparallel paths, one including a frequency signal generator 44 and theother including an intensity signal generator 46. The frequency signalgenerator 44 develops an output signal having a frequency appropriate toa feedback signal that is responsive to the drive signal. The intensitysignal generator develops an output signal having an intensityappropriate to a feedback signal that is responsive to the drive signal.Frequency and intensity parameters may be measured at any point in thesimulator following these generators. The frequency and intensityrepresentative signal are combined by a combiner 47 to produce a signalhaving a frequency and an intensity appropriate to a responsive feedbacksignal. This low level signal is stepped up in voltage by a step-updriver 49 to produce the simulated handpiece feedback signal, which isreturned to the feedback signal input of the handpiece driver.

FIG. 3 is a schematic and block diagram of the handpiece simulator ofFIG. 2. In the following discussion of this FIGURE, the parentheticalnotations are to commercially available integrated circuit device typesthat may be employed in the construction of the simulator. The drivesignal from the handpiece driver is applied to a resistive impedance 42.At test point TP1 is located at the input side of the impedance 42. Thefrequency signal generator 44 is comprised of two parallel paths, theupper one including a diode limiter 60 which clips and squares the inputsignal. The limited signal is amplified by a gain stage 62 (OP27) andthe negative-going portion of the signal is clipped by a diode 64. Theresultant unipolar signal is now in a digital form, and is applied to afrequency to voltage converter 66 (LM2907) which produces a voltageproportionate to the input signal frequency. This voltage is filtered bya low pass filter 68 (324) and applied to a node 72. Also applied to thenode 72 is a pedestal voltage from a reference voltage source 70 (1403;324). The pedestal voltage applied to the node insures that a positivepotential will be present initially at the node. This will providesystem stability in the event that the handpiece simulator is actuatedupon power-up of the module, during which time the feedback loop maystill be in the process of stabilizing. The voltage at the node, whichis a combination of that Produced by the converter 66 and the referencevoltage generator, is coupled by an inverter 74 (324) to a voltage tofrequency converter 76 (2206). The converter 76 will produce an outputsignal with a frequency that is a function of the voltage applied at itsinput. In a constructed embodiment the pedestal voltage was calibratedto produce a 60 KHz signal at the output of the converter 76, and as thevoltage derived from the drive signal began to contribute to the netvoltage at the node 72, driving the net voltage higher, the increasingvoltage at the input of the converter 76 acted to decrease the frequencyof the output signal of the converter as the feedback loop began tostabilize. In a preferred embodiment the reference voltage source isoperated under control of the system controller to apply variouspedestal voltages to the converter 76 depending upon the frequency ofthe handpiece being simulated, or is stepped over a range of pedestalvoltages to exercise and test the response of the handpiece driver todifferent handpiece modes of operation. FIG. 3 also shows the possibleconnection of two test points, TP3A and TP3B, at the input and output ofthe converter 76. The use of these test points will be discussed below.

The frequency signal produced by the converter 76 is applied to theinput of a solid state switch 88 (DG201). The frequency signal will becoupled to the output of the switch 88 depending upon the state of thesignal at the control input of the switch. The control signal for theswitch begins with the drive signal at the impedance 42, which isapplied to a comparator 80 (339). The output of the comparator 80 iscoupled to a missing pulse detector 82 (555) which operates withfeedback provided by a transistor 84. The missing pulse detectordevelops a bistate output signal depending upon the continuous nature ofthe drive signal. If the drive signal is continuous, the detector 82produces a signal of one state; if the drive signal is discontinuous, asignal of the other state is produced. The detector output signal isfiltered by a lowpass filter 86 (339) and is coupled to the controlinput of the switch 88. Thus, if the drive signal is continuous thefrequency signal is passed by the switch; if the drive signal isdiscontinuous, the frequency signal is not passed. The output of theswitch 88 is coupled to the input of a transconductance amplifier 100(CA3080).

The intensity signal generator is shown in the bottom path in thedrawing and has as its input signal the drive signal of the impedanceelement 42. The drive signal is applied to the input of an RMS converter90 (AD536), which has a test point TP2 at its output. The RMS converterprovides a full wave rectification of the input signal and produces a DCoutput signal. This DC signal is buffered by a buffer 92 (CA3146) and isamplified by an amplifier 94 (OP27). The amplified signal is droppedacross a resistor 96 to develop a current, which is applied to the gaincontrol input of the transconductance amplifier. Thus, thetransconductance amplifier receives the frequency signal at its inputand amplifies this signal as a function of the intensity signal appliedto its gain control input. The output signal of the transconductanceamplifier 100 thus has the frequency and intensity characteristics of afeedback signal appropriate to the drive signal from the handpiecedriver. This signal may be measured at test point TP3 at the output ofthe transconductance amplifier 100.

The output signal of the transconductance amplifier 100 is buffered by abuffer 102 (3140) and stepped up in voltage by the step-up driver 49.The buffered signal is applied to the inputs of complementary highcurrent amplifiers 110 and 112. The outputs of amplifiers 110 and 112are coupled to the primary windings of three transformers 114A, 114B,and 114C, which are connected in parallel. The secondary windings of thetransformers are coupled in series to provide the high voltage feedbacksignal which is returned to the handpiece driver.

In operation the handpiece driver may be set to drive a handpiece at agiven intensity and power level, and at a given frequency, for instancein the range of 54-56 KHz. When the handpiece simulator is initiallyconnected to the handpiece driver the start-up drive signal may be inthe range of 40-50 KHz, for example. The feedback signal from thesimulator will thus have a frequency primarily determined by thepedestal voltage, around 60 KHz, and will be of a low intensity andpower. But as the feedback loop of the simulator and driver begins tostabilize, the intensity will increase, thereby increasing the gain ofthe transconductance amplifier, and the frequency will decrease towardthe desired range. When the loop has stabilized, measurements can betaken to ascertain the performance of the loop and the handpiece driver.For instance, the input signal provided by the handpiece driver ispresent at TP1 and the voltage level on the other side of the impedance42 is present at TP2. By converting the signal at TP1 to a DC voltagewith an RMS converter similar to converter 90 and comparing theconverter signal with that present at TP2, the power delivered by thehandpiece driver may be ascertained. The signals present at TP3 and TP3Aprovide information as to the frequency characteristics of the signalprovided by the driver. The signal at TP3 represents the characteristicsof the feedback signal and also the intensity of the driver signal byreason of the intensity control signal supplied to the gain controlinput of the transconductance amplifier. Hence the measurement and useof the signals at the indicated test points may be used to determine thecritical characteristics of the signals provided by the handpiece driver30.

FIG. 4 illustrates an embodiment of a handpiece simulator of the presentinvention in which the system controller 50 includes a microprocessor54. The simulator input signal from the handpiece driver 30 is appliedto the input terminal TP1. The input signal which is nominally a 210volts rms signal at approximately 55 KHz is dropped across resistors 42and 43. A signal at approximately 6-8 volts rms is tapped off at thejunction to the two resistors and applied to the input of a limiter 60as in the embodiment of FIG. 3. The limited signal is buffered by anamplifier 124 and applied to the input of an RMS converter 90 whichproduces a DC signal that is a measure of the voltage of the inputsignal to the simulator. The DC voltage produced by the RMS converter 90is digitized by a 12 bit analog to digital (A to D) converter 132 andthe digital signal samples are applied to one input of a multiplexer136.

In a parallel path the signal produced by the limiter 60 is buffered byan amplifier 62 and converted to a unipolar signal by a diode 64. Theunipolar signal is applied to a frequency to voltage converter 66 whichproduces a DC voltage in the range of 0-10 volts in correspondence to asignal frequency range of 40-60 KHz. The DC voltage produced by theconverter 66 is sampled by a 16 bit A to D converter 134 and the digitalsamples are applied to a second input of the multiplexer 136. Undercontrol of the microprocessor 54 the multiplexer alternately steersdigital samples from the two A to D converters to the microprocessor forstorage and analysis.

Signals representative of the power, intensity and frequencycharacteristics desired of the handpiece drive signal are provided bydriver controls 140. These signals are used to control the handpiecedriver 30, and are also provided to the microprocessor 54 to inform themicroprocessor of the demand placed to the handpiece driver. On thebasis of the required signal characteristics the microprocessor cananalyze the measured voltage and frequency signal samples to ascertainwhether the handpiece driver is operating properly. This may be done bycalculating algorithms using the information received by themicroprocessor, or may be done by comparing the signal samples over timewith table look-up values to see that the sampled signal characteristicsare within acceptable limits. If the received signals are found to beoutside the ranges of acceptable levels the microprocessor will send anappropriate signal to a display 52 to inform the user of the signalcharacteristic found to be deficient.

The microprocessor 54 will also use the information it receives toproduce necessary signal components for the generation of a feedbacksignal to be returned to the handpiece driver. A 16 bit digital signalrepresentative of the frequency of the feedback signal is applied to theinput of a digital to analog (D to A) converter 142. The output of the Dto A converter 142, typically in the range of 0 to 10 volts, is appliedto a voltage to frequency converter 144 which generates an a.c. signalin a typical frequency range of 40-60 KHz. The output signal of theconverter 144 is applied to the input of transconductance amplifier 100.An 8 bit digital signal representative of the gain control signal forthe transconductance amplifier is applied by the microprocessor to theinput of a D to A converter 146. The gain control output voltageproduced by the D to A converter 146 has a typical dynamic range of 20volts and is applied to the gain control input of the transconductanceamplifier 100. The illustrated components following the transconductanceamplifier and used to produce the feedback signal for the handpiecedriver function in the same manner as in the embodiment of FIG. 3.

As mentioned above, the results of the analysis and comparisons made bythe microprocessor 54 are displayed to the user on a display 52 undercontrol of the microprocessor. The display could simply illuminateselectively a red or a green light or LED for each function, therebyinforming the user not only whether the handpiece driver is functioningproperly, but the signal characteristic(s) which is the source of aproblem. The latter information is of considerable assistance to arepairman who is repairing a system which has failed in a particularrespect. In a preferred embodiment the display would be an alphanumericliquid crystal display which displays not only system performance asbeing within or outside the predetermined system limits, but also aquantified representation of system performance. As an example, such adisplay would show the exact frequency at which the driver-simulatorloop stabilized. The microprocessor 54 could also be used in conjunctionwith the analog embodiment of FIG. 3 to produce output signals forcontrol of reference voltage generator 70 to step the pedestal voltageover a range of frequency-representative voltages. In the embodiment ofFIG. 4 such stepping of the frequency would be accomplished by steppingthe digital values applied to the D to A converter 142. In either case,such frequency stepping would exercise the handpiece driver so as todetermine the driver's response to a sequence of simulated frequencyvalue offsets of a phacoemulsification handpiece, such as those that mayoccur during use of a handpiece in opthalmic surgery.

What is claimed is:
 1. A handpiece driver system for emulsifying tissue during surgery comprising:a handpiece driver having an electrical output, the output of said driver producing an electrical drive signal controlled by a control means and electrically connected to a handpiece, a feedback loop electrically connecting said handpiece, driver and control means; a handpiece simulator; means for selectively, electrically switching said handpiece or said handpiece simulator into said feedback loop with said handpiece driver and control means; and said handpiece simulator including means for electrically replacing said handpiece in said feedback loop containing said handpiece driver and said control means, said handpiece simulator including means for receiving a drive signal from said handpiece driver and containing a frequency generator means for producing a frequency appropriate to a feedback signal responsive to the drive signal and an intensity signal generator means for producing an intensity appropriate to a feedback signal also responsive to said drive signal, said handpiece simulator further comprising a means for electrically combining said frequency and intensity signals to generate an electrical feedback signal to said handpiece driver in electrical connection therewith, and said handpiece simulator including means for providing an indication to a user of the performance of said handpiece driver.
 2. The system of claim 1, wherein said handpiece simulator further includes means, responsive to said drive signal, for inhibiting said feedback signal in the presence of a discontinuous drive signal.
 3. The system of claim 1, wherein said handpiece simulator further includes means for offsetting the frequency of said feedback signal as a function of said drive signal.
 4. The system of claim 1, further including driver controls and a display, coupled to said handpiece driver and said control means, said driver controls including means for controlling said handpiece driver and said display including means for displaying signal characteristics provided to said control means.
 5. The system of claim 1, wherein said control means includes a microprocessor, responsive to electrical characteristics of said drive signal, for providing said feedback signal.
 6. The system of claim 5, wherein said control means controls said display means to provide indications of the power, frequency, and intensity characteristics of said drive signal. 